Many commercial products are temperature sensitive and can spoil, deteriorate or lose quality if they suffer even brief exposure to a temperature near or below freezing. For example, fruits may turn brown, flowers, salad greens and some herbs may wilt and vaccines may lose potency. Some other freeze-sensitive products include pharmaceutical products, medications, blood products, and health care products containing freeze-sensitive products such as natural, synthetic or recombinant proteins and polypeptides, as well as foodstuffs, beverages, and some industrial products, for example emulsions, and latex paints. Some products can suffer a loss of quality owing to exposure to an unduly cold temperature, without exhibiting any clear change in appearance.
To help monitor the possible presence of such invisible, or hidden, loss of quality, low-cost freeze indicators can be employed. One useful freeze indicator can provide an irreversible indication of past exposure of the host product to freezing or near freezing temperatures and can be associated with a freeze-sensitive host product, for example by attaching the freeze indicator to the host product.
Various proposals for such freeze indicators are known. For example, U.S. Pat. Nos. 7,343,872 and 7,490,575 and U.S. Patent Application Publications Nos. 2008/0110391 and 2008/0257251, all having inventors Taylor et al., disclose a variety of freeze indicators and freeze indicator technologies. These patents and patent application publications are referenced herein as the “Taylor et al. patent publications”. U.S. Patent Application Publication No. US 2010/0162941, to Lentz et al. also discloses a variety of freeze indicators and freeze indicator technologies. Each of the Taylor et al. patent publications and the Lentz et al. application are incorporated by reference herein.
As described in their specifications the Taylor et al. patent publications and the Lentz et al. application disclose freeze indicators which employ an indicator element comprising a dispersion of solid particles in a liquid medium. The indicator element can change appearance irreversibly upon exposure to freezing temperatures, for example as a result of coagulation of the dispersed solid particles, providing a signal that the freeze indicator has been exposed to a freezing temperature.
Furthermore, U.S. Pat. No. 6,957,623 to Guisinger describes a critical temperature indicator which produces a visual, irreversible indication that the indicator has been exposed to a critical temperature such as a temperature near the freezing point of water. As described in its specification, Guisinger's critical temperature indicator includes a transformable material including a mixture of water, a nucleating agent, latex, and a stabilizer for the nucleating agent. Also as described, the latex can be a wax, the nucleating agent can be an ice nucleating active (INA) microorganism and the water can comprise deuterium oxide.
Notwithstanding the foregoing proposals for freeze indicators it would be desirable to have a freeze indicator having enhanced response characteristics.